Polygons with holes are now rendered correctly (#513)

Author: timtreis

src/spatialdata_plot/pl/render.py

@@ -55,6 +55,7 @@
     _prepare_transformation,
     _rasterize_if_necessary,
     _set_color_source_vec,
+    _validate_polygons,
 )
 
 _Normalize = Normalize | abc.Sequence[Normalize]
@@ -183,6 +184,8 @@ def _render_shapes(
             )
             shapes = _convert_shapes(shapes, render_params.shape, max_extent)
 
+    shapes = _validate_polygons(shapes)
+
     # Determine which method to use for rendering
     method = render_params.method
 

src/spatialdata_plot/pl/utils.py

@@ -1545,6 +1545,38 @@ def _get_linear_colormap(colors: list[str], background: str) -> list[LinearSegme
     return [LinearSegmentedColormap.from_list(c, [background, c], N=256) for c in colors]
 
 
+def _validate_polygons(shapes: GeoDataFrame) -> GeoDataFrame:
+    """
+    Convert Polygons with holes to MultiPolygons to keep interior rings during rendering.
+
+    Parameters
+    ----------
+    shapes
+        GeoDataFrame containing a `geometry` column.
+
+    Returns
+    -------
+    GeoDataFrame
+        ``shapes`` with holed Polygons converted to MultiPolygons.
+    """
+    if "geometry" not in shapes:
+        return shapes
+
+    converted_count = 0
+    for idx, geom in shapes["geometry"].items():
+        if isinstance(geom, shapely.Polygon) and len(geom.interiors) > 0:
+            shapes.at[idx, "geometry"] = shapely.MultiPolygon([geom])
+            converted_count += 1
+
+    if converted_count > 0:
+        logger.info(
+            "Converted %d Polygon(s) with holes to MultiPolygon(s) for correct rendering.",
+            converted_count,
+        )
+
+    return shapes
+
+
 def _collect_polygon_rings(
     geom: shapely.Polygon | shapely.MultiPolygon,
 ) -> list[tuple[np.ndarray, list[np.ndarray]]]:

tests/_images/Shapes_can_render_multipolygons_that_say_they_are_polygons.png

@@ -116,6 +116,20 @@ def test_plot_can_render_multipolygons_with_multiple_holes(self):
 
         fig.tight_layout()
 
+    def test_plot_can_render_multipolygons_that_say_they_are_polygons(self):
+        exterior = [(0, 0), (0, 1), (1, 1), (1, 0), (0, 0)]
+        interior = [(0.1, 0.1), (0.1, 0.9), (0.9, 0.9), (0.9, 0.1), (0.1, 0.1)]
+        polygon = Polygon(exterior, [interior])
+        geo_df = gpd.GeoDataFrame(geometry=[polygon])
+        sdata = SpatialData(shapes={"test": ShapesModel.parse(geo_df)})
+
+        fig, ax = plt.subplots()
+        sdata.pl.render_shapes(element="test").pl.show(ax=ax)
+        ax.set_xlim(-1, 2)
+        ax.set_ylim(-1, 2)
+
+        fig.tight_layout()
+
     def test_plot_can_color_multipolygons_with_multiple_holes(self):
         square = [(0.0, 0.0), (5.0, 0.0), (5.0, 5.0), (0.0, 5.0), (0.0, 0.0)]
         first_hole = [(1.0, 1.0), (2.0, 1.0), (2.0, 2.0), (1.0, 2.0), (1.0, 1.0)]